There is a liquid crystal optical device that changes the distribution of the refractive index according to an applied voltage by utilizing the birefringence of a liquid crystal. There is a stereoscopic image display device in which such a liquid crystal optical device is combined with an image display unit.
For example, by changing the distribution of the refractive index of the liquid crystal optical device, such an image display device switches between a state in which the image displayed by the image display unit is caused to be incident on the eyes of a viewer as displayed by the image display unit and a state in which the image displayed by the image display unit is caused to be incident on the eyes of the viewer as multiple parallax images. Thereby, a high definition two-dimensional image display operation and a three-dimensional image display operation are performed, where the three-dimensional image display operation includes stereoscopic viewing with the naked eyes due to the multiple parallax images. A liquid crystal optical device and an image display device that are easier to use are desirable.